The present invention relates in general to cooling of internal combustion engines, and, more specifically, to a coolant circuit with flow into the engine being diverted between the cylinder head and the cylinder block according to the operating conditions of the engine.
The invention is an improvement to a liquid-cooled internal combustion engine having at least one cylinder head and one cylinder block, in which                the at least one cylinder head is equipped with at least one integrated coolant jacket, said first coolant jacket having, at the inlet side, a first supply opening for the feed of coolant and, at the outlet side, a first discharge opening for the discharge of the coolant,        the cylinder block is equipped with at least one integrated coolant jacket, said second coolant jacket having, at the inlet side, a second supply opening for the feed of coolant and, at the outlet side, a second discharge opening for the discharge of the coolant,        to form a coolant circuit, the discharge openings can be connected to the supply openings via a recirculation line, a heat exchanger being provided in the recirculation line, and        a pump for delivering coolant is provided at the inlet side.        
An internal combustion engine of the above-stated type is used for example as a drive for a motor vehicle. Within the context of the present invention, the expression “internal combustion engine” encompasses diesel engines and spark-ignition engines and also hybrid internal combustion engines.
It is basically possible for the cooling arrangement of an internal combustion engine to take the form of an air-type cooling arrangement or a liquid-type cooling arrangement. On account of the higher heat capacity of liquids, it is possible for significantly greater quantities of heat to be dissipated using a liquid-type cooling arrangement than is possible using an air-type cooling arrangement. Therefore, internal combustion engines according to the prior art are ever more frequently being equipped with a liquid-type cooling arrangement, because the thermal loading of the engines is constantly increasing. Another reason for this is that internal combustion engines are increasingly being supercharged and—with the aim of obtaining the densest packaging possible—an ever greater number of components are being integrated into the cylinder head or cylinder block, as a result of which the thermal loading of the engines, that is to say of the internal combustion engines, is increasing. The exhaust manifold is increasingly being integrated into the cylinder head in order to be incorporated into a cooling arrangement provided in the cylinder head and in order that the manifold need not be produced from thermally highly loadable materials, which are expensive.
The formation of a liquid-type cooling arrangement necessitates that the cylinder head be equipped with at least one coolant jacket, that is to say necessitates the provision of coolant ducts which conduct the coolant through the cylinder head. The at least one coolant jacket is fed with coolant at the inlet side via a supply opening, which coolant, after flowing through the cylinder head, exits the coolant jacket at the outlet side via a discharge opening. The heat need not first be conducted to the cylinder head surface in order to be dissipated, as is the case in an air-type cooling arrangement, but rather is discharged to the coolant already in the interior of the cylinder head. Here, the coolant is delivered by means of a pump arranged in the coolant circuit, such that said coolant circulates. The heat which is discharged to the coolant is thereby discharged from the interior of the cylinder head via the discharge opening, and is extracted from the coolant again outside the cylinder head, for example by means of a heat exchanger and/or in some other way, for example by means of a heater in the passenger compartment of a vehicle.
Like the cylinder head, the cylinder block may also be equipped with one or more coolant jackets. The cylinder head is however the thermally more highly loaded component because, by contrast to the cylinder block, the head is provided with exhaust-gas-conducting lines, and the combustion chamber walls which are integrated in the head are exposed to hot exhaust gas for longer than the cylinder barrels or liners provided in the cylinder block. Furthermore, the cylinder head has a lower component mass than the block.
For coolant, a water-glycol mixture provided with additives is generally used. Compared to other coolants, water has the advantage that it is non-toxic, readily available and cheap, and furthermore has a very high heat capacity, for which reason water is suitable for the extraction and dissipation of very large amounts of heat, which is generally considered to be advantageous.
To form a coolant circuit, the outlet-side discharge openings via which coolant is discharged from the coolant jackets are connected via a recirculation line to the inlet-side supply openings which serve for the feed of coolant. Here, the recirculation line need not be a line in the physical sense but rather may also be integrated in portions into the cylinder head, the cylinder block or some other component. A heat exchanger is provided in the return line, which heat exchanger extracts heat from the coolant again.
It is not the aim and the purpose of a liquid-type cooling arrangement to extract the greatest possible amount of heat from the internal combustion engine under all operating conditions. In fact, what is sought is demand-dependent control of the liquid-type cooling arrangement, which aside from full load also makes allowance for the operating modes of the internal combustion engine in which it is more advantageous for less heat, or as little heat as possible, to be extracted from the internal combustion engine.
To reduce the friction losses and thus the fuel consumption of an internal combustion engine, fast heating of the engine oil, in particular after a cold start, may be expedient. Fast heating of the engine oil during the warm-up phase of the internal combustion engine ensures a correspondingly fast decrease in the viscosity of the oil and thus a reduction in friction and friction losses, in particular in the bearings which are supplied with oil, for example the bearings of the crankshaft.
Known from the prior art are concepts by means of which the friction losses are reduced by means of fast heating of the engine oil. The oil may for example be actively heated by means of an external heating device. A heating device is however an additional consumer with regard to the usage of fuel, which opposes a reduction in fuel consumption. Other concepts provide that the engine oil heated during operation be stored in an insulated vessel and utilized upon a restart, wherein the oil heated during operation cannot be held at a high temperature for an unlimited amount of time. In a further concept, in the warm-up phase, a coolant-operated oil cooler is utilized, contrary to its intended purpose, for heating the oil, though this in turn assumes fast heating of the coolant.
Fast heating of the engine oil in order to reduce friction losses may basically also be abetted by means of fast heating of the internal combustion engine itself, which in turn is assisted, that is to say forced, by virtue of as little heat as possible being extracted from the internal combustion engine during the warm-up phase. In this respect, the warm-up phase of the internal combustion engine after a cold start is an example of an operating mode in which it is advantageous for as little heat as possible, preferably no heat, to be extracted from the internal combustion engine.
Control of the liquid-type cooling arrangement in which the extraction of heat after a cold start is reduced for the purpose of fast heating of the internal combustion engine may be realized through the use of a temperature-dependently self-controlling valve, often referred to as a thermostat valve. A thermostat valve of said type has a temperature-reactive element which is impinged on by coolant, wherein a line which leads through the valve is blocked or opened up—to a greater or lesser extent—at the element as a function of the coolant temperature.
In an internal combustion engine which has both a liquid-cooled cylinder head and also a liquid-cooled cylinder block, like the internal combustion engine which is the subject of the present invention, it is advantageous for the coolant throughput through the cylinder head and the cylinder block to be controlled independently of one another, in particular because the two components are thermally loaded to different degrees and exhibit different warm-up behavior. In this regard, it would be expedient for the coolant flow through the cylinder head and the coolant flow through the cylinder block to be controlled in each case by means of a dedicated thermostat valve.
U.S. Pat. No. 6,595,164 describes a cooling system for an internal combustion engine, which is cooled by means of liquid coolant, of a motor vehicle. To predefine the quantities of coolant which flow firstly through coolant ducts of a cylinder head and secondly through coolant ducts of a cylinder block, in each case dedicated thermostat valves are positioned downstream of the cylinder head and downstream of the cylinder block. Here, the thermostat valve of the cylinder head has a lower opening temperature than the thermostat valve of the cylinder block.
A disadvantage of the control as per U.S. Pat. No. 6,595,164 is that two shut-off elements, that is to say two thermostat valves, are required. This increases the costs of the control, the space requirement and the weight. A further disadvantage of the described control is that the circulation of the coolant in the cooling circuit, that is to say the flow of coolant, cannot be prevented in a targeted manner, not even after a cold start of the internal combustion engine. Therefore, after a cold start, coolant is conducted both through the cylinder head and also through the cylinder block, although the coolant flow through the cylinder block is reduced to a small leakage flow. A reduction of the dissipation of heat by convection is realized primarily through the bypassing of a coolant cooler arranged in the circuit, wherein the coolant conducted through the cylinder head is not conducted through the cooler in any switching state of the thermostat valves, and the coolant of the cylinder block is conducted through the cooler only when the opening temperature of the associated thermostat valve is reached.
By contrast, if, at least at the start of the warm-up phase, the coolant did not flow but rather was stationary in the lines and in the coolant jacket of the cylinder head and/or of the cylinder block, the warming of the coolant and the heating of the internal combustion engine would be further accelerated. Such control would additionally promote the warming of the engine oil and further reduce friction losses.
Furthermore, control of the liquid-type cooling arrangement is basically sought with which not only the circulating coolant quantity or the coolant throughput can be reduced after a cold start, but rather also the thermal management of the internal combustion engine heated up to operating temperature can be influenced.
A self-controlling thermostat valve with an invariant, component-specific operating temperature must be suitable for all load states and therefore have an opening temperature configured for high loads, which is comparatively low and leads to relatively low coolant temperatures even in part-load operation.
Different coolant temperatures would however be advantageous for different load states, because the heat transfer in the cylinder head is determined not only by the throughput coolant quantity but rather significantly also by the temperature difference between the component and coolant. A relatively high coolant temperature in part-load operation is thus equivalent to a small temperature difference between the coolant and the cylinder head or cylinder block. The result is reduced heat transfer at low and medium loads. This increases efficiency in part-load operation.